Known as a conventional spectroscopic sensor is one comprising an interference filter unit for transmitting therethrough light having a predetermined wavelength according to an incident position of light, a light-transmitting substrate for transmitting therethrough the light incident on the interference filter unit, and a light-detecting substrate for detecting the light transmitted through the interference filter unit. Here, a pair of mirror layers may oppose each other through a cavity layer so as to construct the interference filter unit as that of Fabry-Perot type (see, for example, Patent Literatures 1 and 2).